Stannous ions (divalent) are susceptible to oxidation by atmospheric oxygen, particularly in the mainly aqueous media found in these compositions. The oxidation gives stannic ions (tetravalent) which extensively hydrolyze in the aqueous medium to form insoluble hydroxo or oxide species which lead to precipitates and turbidity. This is unwanted e.g. for any quantitative stannous ion analytics of oral care formulations, which accordingly must be done with exclusion of atmospheric oxygen to prevent loss of soluble, quantifiable stannous ions as precipitated, not easily quantifiable, stannic ions.